1. Technical Field
The present disclosure relates to plasma processing equipment and, more particularly, to a structure for preventing gap formation, which prevents plasma deposition in the space between a chuck and a ring, and plasma processing equipment having the same.
2. Discussion of Related Art
Generally, a semiconductor device is fabricated by selectively and repeatedly performing certain fabrication processes, such as photolithography, etching, ashing, diffusion, chemical vapor deposition, ion implantation, metal deposition, and the like, on a wafer.
Among the aforementioned semiconductor device fabrication processes, an etching process is divided into a wet etching process and a dry etching process.
The dry etching process etches a layer material formed on a wafer, by supplying a reactive gas into a chamber to form plasma in the chamber, and using a chemical and physical reaction of reactive ions to perform the etching.
FIG. 1 is a sectional view of conventional plasma processing equipment used for a dry etching process.
In FIG. 1, the conventional plasma processing equipment comprises: a chamber, an electrostatic chuck, an upper electrode, and a gas supply unit. The electrostatic chuck is positioned inside the chamber, holds a wafer on which a layer material is formed, and has a lower electrode. The upper electrode is positioned in the chamber to be above the electrostatic chuck. The gas supply unit supplies a reactive gas into the chamber.
Therefore, when the reactive gas is supplied from the gas supply unit into the chamber and RF power is applied from an external power source to the upper and lower electrodes, a plasma environment is formed inside the chamber.
Specifically, the conventional plasma processing equipment includes a focus ring at an outer side of the electrostatic chuck. The focus ring is composed of a silicon material and surrounds the outer side of the electrostatic chuck. Therefore, the focus ring allows a plasma generation region to be uniformly formed on the wafer held on the electrostatic chuck.
A number of rings are positioned around the focus ring. This constitution will be described in more detail hereinbelow.
As illustrated in FIG. 1, the electrostatic chuck 20 has a stepped part around its outside circumference. The focus ring 30 is positioned on the stepped part. A number of other rings are positioned at an outer side of the focus ring 30. These other rings are positioned at the outside circumference of the electrostatic chuck 20 and include a holder ring 50 positioned under the focus ring 30, an outer ring positioned at an outer side of the holder ring 50, and a cover ring positioned on the outer ring and covering the outer side of the focus ring.
A gap is formed in the spaces between the outer circumference surfaces of the holder ring 50 and the focus ring 30 and between the rings, thereby forming channels, as represented by the arrows shown in FIG. 1. A gap is present that is an exhaust channel through which the gas is exhausted after the process is performed inside the chamber.
Among the conventional plasma processing equipment, the Me_SCCM equipment of TEL includes a rubber element 31 composed of the silicon (Si) material. The rubber element 31 is interposed between the electrostatic chuck 20 and the focus ring 30 to improve thermal conductivity of the focus ring 30.
The rubber element 31 is interposed between the bottom surface of the focus ring 30 and the stepped part of the electrostatic chuck 20, as illustrated in FIG. 1.
An operation of the conventional plasma processing equipment in the aforementioned constitution will be described below.
Referring to FIG. 1, an external power supply (not shown) applies the RF power to the upper and lower electrodes (not shown). The gas supply unit supplies the reactive gas into the chamber. Therefore, the reactive gas supplied into the chamber is formed as plasma inside the chamber by the RF power. Reaction ions of the plasma are attracted towards the wafer W by the self bias electric potential of the wafer, and the attracted reaction ions etch the layer material formed on the wafer W.
Then, the reaction ions etch an inner circumference surface of the focus ring 30 and an outer circumference surface of the electrostatic chuck 20 that are in contact with each other, to form a gap B between the inner circumference surface of the focus ring 30 and the outer circumference surface of the electrostatic chuck 20. Therefore, in the conventional plasma processing equipment, because the reaction ions introduced through the gap B flow along the channel following the arrow directions shown in FIG. 1, the rubber element 31 positioned at the stepped part of the electrostatic chuck 20 becomes burned.
Moreover, after etching, the reaction ions pass through the channel along the direction of the arrows, to be exhausted outside the chamber. Then, in the conventional plasma processing equipment, after the reaction at high temperatures, the reaction ions burn the rubber element 31, as indicated above.
Furthermore, in the conventional plasma processing equipment, polymers or other byproducts, which are generated when the layer material formed on the wafer W is etched by the reaction ions, accumulate or flow into the inside of the channel along the direction of the arrows shown in FIG. 1.